Re: [Boost-Users] operator == in shared_ptr

From: Johan Ericsson (johanericsson_at_[hidden])
Date: 2002-04-29 23:45:10

Use std::find_if, and pass it a predicate function or
function object. That is the standard way that you
override the equality function if it doesn't do what
you want.

http://www.sgi.com/tech/stl/find_if.html

This function object should work nicely:

// warning unchecked code
template<class T>
struct DerefCompare
{
   bool operator()(boost::shared_ptr<T> t) const
   {
     return ((*t)==val);
   }
   DerefCompare(T inVal):val(inVal){}
   T val;
};

template <class T>
DerefCompare<T> make_deref(T t)
{
    return DerefCompare<T>(t);
}

Then to use it, use syntax like:

std::find_if(vec.begin(),vec.end(),make_deref(5));

Johan
--- sashan <sashang_at_[hidden]> wrote:
> Hi
> 
> Because the operator== function compares pointers
> and not what they're pointing to this is what I've
> had to do to get it to find an integer. Basically I
> had to wrap the basic int type within another class
> called Int, as show below.
> 
> class Int
> {
> private:
>  shared_ptr<int> p;
> 
> public:
>  Int(int i) {p.reset(new int); *p = i;}
>  bool operator==(const Int& r) {return *p.get() ==
> *r.p.get();}
>  ~Int() {};
> };
> 
> void main()
> {
>  vector < Int > vec;
>  vec.push_back(Int(1));
>  vec.push_back(Int(2));
>  vec.push_back(Int(3));
>  Int p(4); 
>  if (find(vec.begin(), vec.end(), p) == vec.end())
>  {
>   cout << "Couldn't find it";
>  }
> }
> 
> Is there a better way that doesn't involve 1) having
> to write a wrapper class around a basic type (or any
> type) and 2) doesn't involve changing the
> shared_ptr::operator==.
> 
> 
> 
> [Non-text portions of this message have been
> removed]
> 
> 
> 

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